Emptying page cache and Data Base Cache Error

First, emptying page caches takes very long time than before and often ends up with blank white page. After second and third attempt cleaning caches, I got the message that caches are emptied successfully.

Secondly, while disabling Data Base Cache the following error is populated:
[an error occurred while processing this directive]. After refreshing the plugin page, it looks like the data base has been disabled successfully (at least the box is unchecked).